Sampling tone generator system for electronic organs



Nov. 28, 1967 W MUNCH, JR ET AL 3,355,539

SANPLING TONE GENERATOR SYSTEM EOE ELECTRONIC OReANs Filed Sept. 27, 1963 2 Sheets-Sheet 1 nurse ,10 l

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SAMPLING TONE GENERATOR SYSTEM FOR ELECTRONIC ORGANS 2 Sheets-Sheet 2 Filed Sept. 27, 1963 INVENTUM WILL/.an H. besan/ United States Patent O 3,355,539 SAMPLING TUNE GENERATOR SYSTEM FOR ELECTRNlC GRGANS Walter Munch, Jr., Park Hills, Ky., and Alfred W. Scheide, Cincinnati, Ohio, assignors to D. H. Baldwin Company, Cincinnati, Ohio, a corporation of Qhio Filed Sept. 27, 1963, Ser. No. 312,159 14 Claims. (Cl. SLi-L23) The present invention relates generally to electronic organs, and more particularly to heterodyne tone generation systems for electronic organs.

In the usual tone generator of an electronic organ, an array of oscillators is provided which operates at tone frequency and accordingly it is essential to provide at least one oscillator for each note, or twelve per octave. In accordance with the present invention on the other hand, an array of n oscillators provides frequency components for each of n octaves, and a further array of twelve oscillators provides further components for each of the twelve notes of one octave. The various components are selectively combined in sampling devices, which provide audio tones. A complete array of six octaves of tones can be generated by six harmonic oscillators and twelve further harmonic oscillators, each of the tones comprising an array of harmonics. Thereby, considerable reduction of components of the tone generator of an electronic organ can be achieved.

In accordance with the invention, an array of octave oscillators is provided, one for each octave of a tone generator. Each oscillator generates a gamut of harmonically related frequencies. These frequencies may be described by their fundamentals, F, 2F, 4F, 8F, 16F, 32P, in a six octave generator. Associated with the array of octave oscillators are twelve note oscillators. These oscillators generate extremely short pulses, and therefore gamuts of harmonically related frequencies. The fundamentals of the note oscillators differ from the frequency F by amounts equal to the frequencies of notes of the musical scale. For example if F=20 kc., the frequency of the note oscillator A pertaining to all notes of nomenclature A, has a frequency of 20.110 kc., i.e. F +A. The gamut of notes A are then generated by sampling note oscillator A with selected ones of the octave oscillators. If octave oscillator F is selected, the lowest A of the organ will sound, while if 32F is selected, the highest.

The system not only has the advantage of minimizing the number of oscillators required in a tone generator, but easily permits the paralleling of octave and/ or note oscillators which are slightly dierent in frequencies, with consequent attainment of pipe organ or chorus effect. Since only six octave oscillators are required, these may be free running, if desired, without introducing problems of tuning many oscillators, as is the case in a conventional oscillator. Whereas, in a conventional organ using frequency divider chains to generate the entire required gamutof musical tones phase locking of the notes is present, the present system inherently reduces phase locking to notes of one nomenclature, and no two notes of different nomenclature, even where the octave oscillators are phase locked with each other.

A It is, accordingly, a broad object of the invention to provide novel tone generators of electronic organs.

It is another object of the invention to provide a sarnpling tone generator'for an electronic organ, wherein is employed one note oscillator for each tone of a single octave, fand one additional octave oscillator for each octave of the organ, within a tone division, the note and octave oscillations being sampled to 'generate the full gamut of notes of the division.

Itis another object of the invention to provide chorus ICC eiect in electronic organs by duplicating the note oscilla-tors and/or lthe octave oscillators of a samp-ling tone generator.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

FIGURE l is a block diagram of a system for generating the note of one nomenclature, in a sampling tone generator;

FIGURE 2 is a detector used for sampling note and octave oscillations, in the system of FIGURE 1;

FIGURE 3 is a pulse forming network used in the system of FIGURE 1; and

FIGURE 4 is a modification of the system of FIGURE 1, employing independent octave oscillators, and duplicate octave and note oscillators, to achieve maximum chorus efect, and minimum phase lock of notes.

Referring now to the accompanying drawings, in FIG- URE l, 10 is an oscillator generating square pulses. The oscillator 10 drives a chain of dividers, composed of frequency dividers 11, 12, 13, 14 and 15. Divider 15 provides the -lowest frequency output, and is at 20 kc. Dividers 14, 13, 12, and 11 and oscillator 10 have frequencies, respectively, of 40, kc., kc., 160I kc., 320 kc., and 640 kc. The outputs of oscillator 10 and dividers 11-15 are separated by octaves, and hence are called octave oscillators, there being one octave oscillator for each of six octaves. The wave forms at the output of the oscillators lll-15, inclusive may be shaped 4by wave shaping circuits 118, if desired, these being, however, optional. The outputs of the wave Shapers 11S are gamuts of harmonically related frequencies. The outputs of the wave Shapers 118 are selected at will by Ikey switches 20, and collected on a lead 21, which is connected to a sampling detector 22.

To the detector 22 is also connected an oscillation source comprising a stable source such as crystal oscillator 23, drivin-g a frequency divider 24, which in turn supplies relatively short pulses 25 at its output. A pulse .Sharpener 18 is included to provide an extremely short pulse output. The pulse frequency is 20.110 kc. for the example specified, i.e. where F :2O kc., 110 c.p.s. being the freqency A1 of an organ, i.e. A in the lowest octave of a Igiven division.

At the output of detector 22 is provided an audio lilter 26. An A4 key 28 of the keyboard of the organ would close switch 20 of oscillator 12. Oscillator 12 and wave shaping circuit 118 generate complex waves at 160 kc. and oscillator 23 provides very short pulses 25 at 20.110 kc., at the output of the pulse forming circuit 18. An audio difference frequency between harmonic frequencies of the pulses is generated by detector 22 and is selected by LP. iilter 26.

If it were desired to play note A2, the outputs of oscillators 14 and 23 would be combined. If we denominate the fundamental output of oscillator 23 as f1 and that of oscillator 15 as F, then A1=f1-F, where f1 is above F. Obviously f1 could have been chosen below F. A2, on the other hand, equals 2f1-2F, and is 220 c.p.s. Any sampled combinations of NF with nf, where N and n are integers, does not result in an audio frequency unless N and 11 are equal.

It will be clear that multiple keys 20 may be closed simultaneously, to generate combinations of An. Were detector 22 a mere non-linear device, diticulty would ensue if A1 and A3 were attempted at once, in that A3-A1=60 kc.=3F, which would be generated by the detector as a higher order intermodulation product, and would produce in turn, by combination with 3f, an undesired audio sig- 3 nal. To 4avoid this possibility a special detector is employed, illustrated in FIGURE 2.

The wave shaping circuit may be any one of several types of devices, without departing from the true spirit of the invention. For exam-ple, the outputs of oscillators -15 may be converted to shorter pulses, or to sawtooth waves, or filtered to provide sine waves 0r formed arrays of harmonics hav-ing predetermined relative amplitudes. The output of the system, in terms of tonal content is entirely determined bythe character, i.e. frequency values and relative amplitudes of the frequency components, at the outputs of the wave forming circuits. If desired, each wave forming circuit may actually consist of a parallel array of circuits, as 118, 118', each for selecting a different tone type, i.e. ute, diapason and the like, and these may be selected or inserted in circuit by means of switches 119, 120, as shown in FIGURE 4.

FIGURE 1 illustrates how one gamut of notes, i.e. A, is formed. Reference is made to FIGURE 4, for a more complete illustration of an organ.

In the detector of FIGURE 2 the pulses from the note oscillators 23 are used to sample the complex wave forms of the master oscillator and divider chain. The transistor 30 is of NPN type, and includes a collector 31, an emitter 32 and a base 33. The emitter 32 is biased to -1-1 volt, and the collector to -l-lO` volts through a resistance 35. The l|1 volt bias maintains the transistor eut off. A pulse forming ci-rcuit 18, providing a note oscillator pulse output, supplies 6 volt pulses to the base 33, through current 'limiting resistance 36, at terminal 37, and the selected components of the master oscillator-divided chain output is applied at terminal 38, via resistance 40 and capacitor 41 which maintain the latter currents below cut off, so that no current flows into the collector 31 except when the beat oscillator pulses are applied. When conduction occurs base current has two components, i.e. one due to the positive beat oscillator pulse 2-5, and the other due to the octave oscillators. The base current thus varies, during each beat oscillator pulse 25, according to the then amplitude of the octave oscillators. A form of pulse modulation ensues, having an envelope component due to the difference frequencies and representative thereof. These difference frequencies represent a complex spectrum, including audio and supersonic components and the pulses supplied by the detector 22 must contain all these frequencies. Capacitor 42 integrates the amplified current output pulses available at collector 31, and the integrated current is abstracted as a voltage across capacitor 42, and filtered, by audio low pass filter 26. The filtered output is the desired audio tone.

The pulse formers 18 employ a four layer diode 60 (FIGURE 3) as a switching element. The four layer diode has a volt-ampere characteristic like a neon cell in that the diode goes into conduction when a tiring voltage is attained, and thereafter stays in conduction until its voltage is reduced below a fairly critical small value. In the system of FIGURE 3, the negative supply 61 is below firing potential. When a positive pulse P is applied across diode 62 the terminal voltage of four layer diode 60 increases above ring potential and it lires, discharging capacitor 63 through diodes 60, 62 and resistance 64. When the capacitor 63 discharges the diode 60 turns off and the capacitor begins to recharge through resistance 64. Charge time is made suficiently great that the capacitor -63 does not build up to supply voltage before the next trigger pulse arrives. Output is taken on lead 66 across resistance 64, and is positive since discharge current I is toward ground in resistance 64.

In the alternative system of FIGURE 4, the oscillators 70-75 are independent of each other. This reduces phase locking, in the audio output of the system, but is otherwise a matter of choice over the system of FIGURE l. A more important additive feature of FIGURE 4 is that each of oscillators 70-75 is paralleled by an additional oscillator 76-81, nominally of the same frequency, i.e. nF, but

actually very slightly different in frequency, i.e. nF. FIG- URE 4 also indicates how detectors and beat oscillators for various notes, as 90, 91, 92, for the notes A, A# and B may be resist-ance matrixed in an adding circuit 83, and commonly applied to low pass filter S4 for application to power amplifier and speaker 86.

The addition of oscillators 76-81 is particularly valuable since these can be selected in frequency to provide a small difference between F and F', but a :relatively large difference between 32P and 32E', where the oscillators are all independent. Were the oscillators locked in a chain, as in FIGURE 1, this same result would automatically accrue because of the frequency division process which continually divides not only the frequencies but also the difference between nF and nF. This leads to minimum cost for achieving chorus effect, since there are only six octaves to duplicate.

The keying system of FIGURE 4 assumes that actuation of any organ key 28 connects a selected switch, as 20', which selects (l) an octave oscillator, and (2) a note detector, `appropriate to the key. The switches then serve to add the oscillators 76-81 to the system at will, to produce chorus effect.

While we have described and illustrated one specific embodiment of our invention, it will be clear that variations of the details of construction which are specifically illustrated yand described may be resorted to Without departing from the true spirit and scope of the invention as defined in the appended claims.

What we claim is:

1. A tone generating system for an electronic organ, comprising a plurality of supersonic harmonic rich signal sources having fundamental frequencies yarranged at least approximately in octave relationship, at least one narrow pulse signal source generating sampling signals in the form of sharp pulses in a frequency range having `at least one fundamental frequency differing from the lowest fundamental frequency of said plurality of sources by a difference at least approximately equal to the fundamental frequency of ya note in the musical scale, `a sampling device connected to said at least one narrow pulse source, and means for connecting said plurality of signal sources to said sampling device selectively at will in any combination, and means connected to said sampling device for deriving therefrom audio tone components.

2. The combination according to claim 1 wherein said plurality of harmonic rich signal sources comprises a master oscillator and a chain of frequency dividers.

3. The combination according to claim 1 wherein said plurality of sources comprise oscillators only approximately in octave relation.

4. The combination according to claim 1 further comprising means associated with each of said supersonic harmonic rich signal sources for selectively varying the harmonic content of each of said harmonic rich signals to selectively change the tones of said audio tone components.

5. The combination according to claim 1 wherein said plurality of supersonic harmonic -rich signal sources comprises a plurality of independent signal sources to reduce phase locking of said audio tone components.

6. The combination according to claim 1 wherein said means for connecting said plurality of signal sources to said sampling device selectively at will in any combination comprises a plurality of keys, a single key only for each of said plurality of signal sources, one side of each of said keys being connected together and to said sampling device, the other side of each of said keys being connected to a different one of said plurality of signal sources.

'7. A tone generating system for Ian electronic orga-n, comprising a plurality of arrays of harmonic rich supersonic signal sources, each of said arrays having fundamental frequencies arranged in at least approximately octave relation, and the separate arrays of said plurality having similar arrays of fundamental frequencies, a sampling device, a Ifurther sharpy pulse signal source having a fundamental frequency differing from the lowest approximately equal fundamental frequencies of said plurality of sources by a difference at least approximately equal to the fundamental frequency of a note in the musical scale, means connecting said further sharp pulse signal source to said sampling device, means for connecting said plurality of signal sources in any combination to said sampling device selectively at will to be sampled by said sharp pulse signal, and means connected to said sampling device for deriving therefrom harmonic rich audio tone components.

8. The combination according to claim 7 further comprising means associated with each of said arrays of harmonic rich supersonic signal sources for selectively varying the harmonic content of each of said harmonic rich supersonic signals to selectively change the tones of said audio tone components.

9. The combination according to claim 7 wherein said plurality of arrays of harmonic rich supersonic signal sources comprises a plurality of independent signal sources to reduce phase locking of said audio tone components.

10. A tone generating system for an electronic organ, comprising an array of harmonic rich supersonic signal sources having fundamental frequencies arranged in at least approximately octave relationship, a plurality of sampling pulse sources having approximately equal fundamental frequencies diiering from the lowermost fundamental frequency of said array of Sources by amounts at least approximately equal to the fundamental frequencies of notes in the musical scale, a sampling device connected to said sampling pulse sources, means for connecting said array of signal sources to said sampling device in any combination selectively at will, and means for deriving from said sampling device only audio tone components.

11. In a system for generating organ tones, one source of supersonic wave shapes having frequencies F, 2F, 3F further sources of supersonic wave shapes having frequencies nF, ZnF, BnF, Where n assumes a different one of values, 2, 4, 8, 16 in separate ones of said sources, another source of sharp pulse having supersonic frequencies f, 2f, 3f where the difference of f and F is a tone frequency of the musical scale, and sampling means for deriving from said sources at will any one or more of frequency arrays or differences of (l) Z-i-F, 2f-|2F, 3f-1-3F (2) 2f-f-2F, 1H-4F, SH-SF (3) 1H-4F, 8f4-8F, 12H-12F any one or more of the complete arrays (l), (2), (3) representing components of one harmonic rich tone.

12. A tone generating system for an electronic organ, comprising a plurality of harmonic rich supersonic signal sources having fundamental frequencies arranged in at least approximately octave relationship, a plurality of sampling pulse sources having approximately equal fundamental frequencies differing from the lowermost fundamental frequency of said array of sources by amounts at least approximately equal to the fundamental frequencies of notes in the musical scale, a plurality of sampling devices connected one for one to said sampling pulse sources, means for connecting said plurality of signal sources to said plurality of sampling devices in any combination selectively at will, and means for deriving from said plurality of sampling Idevices only audio tone components.

13. The combination according to claim 12 further comprising means associated with each of said harmonic rich supersonic signal sources for selectively varying the harmonic content of said harmonic rich signals to selectively change the tones of said audio tone components.

14. The combination according to claim 12 wherein said plurality of harmonic rich supersonic signal sources comprises a plurality of independent signal sources to reduce phase locking of said audio tone components.

References Cited UNITED STATES PATENTS 1,823,716 9/1931 Young 84-l.23 X 1,823,724 9/ 1931 Carlson Sil- 1.23 2,697,959 12/1954 Kent 328-15 X 3,171,036 2/1965 Sokoler 307-885 OTHER REFERENCES Dorf: Electronic Musical Instruments, Radio Magazines Inc., 1954, page 149 relied on, ML-1092-D57.

ARTHUR GAUSS, Primary Examiner. l. HEYlVlAN, J. EPELL, Assistant Examiners. 

1. A TONE GENERATING SYSTEM FOR AN ELECTRONIC ORGAN, COMPRISING A PLURALITY OF SUPERSONIC HARMONIC RICH SIGNAL SOURCES HAVING FUNDAMENTAL FREQUENCIES ARRANGED AT LEAST APPROXIMATELY IN OCTAVE RELATIONSHIP, AT LEAST ONE NARROW PULSE SIGNAL SOURCE GENERATING SAMPLING SIGNALS IN THE FORM OF SHARP PULSES IN A FREQUENCY RANGE HAVING AT LEAST ONE FUNDAMENTAL FREQUENCY DIFFERING FROM THE LOWEST FUNDAMENTAL FREQUENCY OF SAID PLURALITY OF SOURCES BY A DIFFERENCE AT LEAST APPROXIMATELY EQUAL TO THE FUNDAMENTAL FREQUENCY OF A NOTE IN THE MUSICAL SCALE, A SAMPLING DEVICE CONNECTED TO SAID AT LEAST ONE NARROW PULSE SOURCE, AND MEANS FOR CONNECTING SAID PLURALITY OF SIGNAL SOURCES TO SAID SAMPLING DEVICE SELECTIVELY AT WILL IN ANY COMBINATION, AND MEANS CONNECTED TO SAID SAMPLING DEVICE FOR DERIVING THEREFROM AUDIO TONE COMPONENTS. 